This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Lopinavir/ritonavir is available as an oral solution for pediatric dosing. This liquid formulation has an unpleasant taste, contains 42% alcohol (with the potential to cause significant alcohol toxicity in accidental overdose), must be taken with food, is bulky and requires refrigeration, all of which are barriers to use in pediatric populations. A new film-coated tablet formulation has recently been approved in the U.S. that does not require refrigeration and may be taken without regard to meals. The prescribing information states that these tablets may not be crushed, broken or chewed, and the manufacturer does not plan to examine the pharmacokinetics of crushed tablets at this time. However, patients and caregivers are dosing pediatric patients with crushed tablets to overcome some of the limitations of the oral solution. If crushed tablet administration yields significantly lower systemic exposure to lopinavir than whole tablets, then patients using this administration technique will be at higher risk for development of viral resistance and treatment failure. This administration technique must be studied so that providers have evidence to support recommendations about this dose administration strategy. This study is aimed to describe the pharmacokinetics of lopinavir in pediatric patients after taking the whole tablet formulation and compare within the same subject to the pharmacokinetics after crushing the tablet formulation and mixing with pudding or yogurt. It is hypothesized that Lopinavir exposure in pediatric patients will be lower after taking a dose of the tablet formulation, crushed and mixed with pudding or yogurt, as compared to the exposure after taking a dose with tablets swallowed whole.